This section is from the book "Cyclopedia Of Architecture, Carpentry, And Building", by James C. et al. Also available from Amazon: Cyclopedia Of Architecture, Carpentry And Building.
The first operation in connection with the application of the finish is that of covering the framework with sheathing, which should be about 1 inch in thickness, and for the best work, dressed on one side. The sheathing should be placed diagonally across the studding when the frame is of the "balloon" variety, but in case of a braced frame the boards need not be so placed. With the braced frame, the boarding may be started at any time, but with the balloon frame it is necessary to wait until all of the studding has been placed in the outside walls. The sheathing should be laid close, but need not be matched, and the boards should be fairly wide, say 8 to 10 inches, or even more. The most common material for this work is yellow pine free from loose knots. Spruce or hemlock may be used with good results.
Copyright, 1912, by American School of Correspondence.
The roof sheathing is nailed on at right angles to the rafters but the boards are narrower. The width is usually 4 inches but 6 inches works well also. They are laid with spaces between them for the passage of air. These spaces are from 2 to 3 inches wide and are left for the ventilation of the shingling or other roof covering, and for the cheapening of the rough boarding.
Roof boarding is not laid diagonally, but if this were done a very much stronger building would be obtained than where the boarding is laid horizontally, because each board acts somewhat as a truss to bind the whole framework more securely together. Some curved work, such as round towers and bay windows, is boarded diagonally, when it is impossible to place the boards in any other way. Each piece should be well nailed to each stud or rafter with large nails, ten-penny or eight-penny, and no serious defects such as large knots should be allowed in the sheathing.